Natural gas typically requires treatment to remove acid gas contamination including carbon dioxide (CO2) and hydrogen sulfide (H2S) before utilization of the natural gas. As natural gas production continues to grow in remote areas and in gas fields containing acid gases, there is a need to treat natural gas produced from these fields using efficient methods to remove such contaminants. To treat acid gases, aqueous amine absorption is the standard technology because of high recovery of hydrocarbons and efficient energy use. However, amine absorption technology may not be feasible or practical when treating natural gas at the well head or at low flow rates. Amine absorption technology has issues associated with handling solvents required for regeneration, and has poor economics in remote or offshore locations. Practical use of amine absorption technology would require absorption of acid gases at mild temperatures, heating the solvent to high temperatures to remove the acid gases in a stripping tower, and subsequent cooling of the solvent to return to the absorption unit. The natural gas product from the amine unit further requires a dehydration step to remove water for dew point control.
Pressure-swing adsorption (PSA) technology is an alternative technology for treating natural gas that uses a solid adsorbent material to remove acid gases. PSA technology operates by using an adsorbent material that removes a target adsorbate molecule from a gas mixture by preferential adsorption over other species in the gas mixture. Adsorption processes that remove CO2 from gas streams typically use zeolite- or carbon-based adsorbent materials. The adsorbent can either function by equilibrium (thermodynamics) or kinetic (rate-based) separations. In principle, all adsorption processes utilize at least two steps: adsorption or uptake of the target molecule in the adsorbent; and desorption or removal of that same target molecule from the adsorbent. This may be achieved by changes in concentration, pressure, or temperature. In the case of PSA and vacuum-swing adsorption (VSA), pressure changes are used to regenerate the adsorbent. PSA does not require a dehydration step. PSA technology is able to treat natural gas containing acid gases without the need for on-site solvent regeneration and other issues associated with amine units.
It would be desirable to have a PSA process utilizing an adsorbent material which would require lower vacuum power consumption and which would allow improved hydrocarbon recoveries as compared with known processes. Such a process would enable deployment and competitive use of PSA units for natural gas separations in expanded applications.